1. Field of the Invention
The present invention relates generally to powder compositions for use in human skin care. In particular, the present invention relates to a moisture-absorbing powder composition suitable for topical application to the skin comprising croscarmellose sodium.
2. Background
A number of materials, and for example, talc and topical starch, have long been used in pharmaceutical and cosmetic preparations as protective agents on skin areas exposed to excessive moisture or perspiration. Powder compositions containing talc and topical starch are used for absorbing moisture resulting from the action of the sebaceous and sweat glands. Body powders are frequently used on infants to help prevent diaper rash and otherwise help maintain dryness. Powders are also used in foot care, feminine hygiene, antiperspirants and general cosmetic products. Powders have also been incorporated into creams, ointments, solid sticks or compacts.
Talc is widely employed in skin care compositions, including powder compositions, because of its water repellent action, emollience and slip characteristics which lubricate skin surfaces. Its emollience and slip properties give talc its superior "skin feel" properties. Thus, talc is used in the formulation of cosmetics and as a powder for treating tender skin to prevent chafing and other irritation such as would occur from diapers or wet clothing. However, its ability to absorb aqueous fluids is quite limited. Compared to topical starch, which can absorb up to about 25 wt. % of aqueous fluids, talc has insignificant fluid-absorption capacity.
The advantages of combining the absorptive action of topical starch with the emollience and lubricity of talc or other skin protectant agents have been previously recognized. By way of example, Harvey (U.S. Pat. No. 4,913,896) discloses a powder that contains talc (65-80%) and starch (20-30%) together with antibacterial and/or antifungal agents. Whistler (U.S. Pat. No. 5,453,281) substitutes small granule starch for binder excipients in pills or cosmetic and/or dusting powder compositions. However, the total absorptivity (i.e., fluid-absorption capacity) of the composition is generally unsatisfactory unless substantial amounts of starch are employed. However, if the composition contains a high proportion of starch to maintain the desired absorptivity, then the beneficial attributes provided by the other agents in the composition, such as skin feel in the case of talc, are compromised.
Attempts have been made to improve the moisture absorbency properties of compositions containing talc and topical starch. For example, pregelatinized starch has been added as a minor component to talc or starch (Ashton et al., U.S. Pat. Nos. 4,485,092 and 4,568,539; Harvey, U.S. Pat. No. 4,913,896) for the purpose of increasing moisture absorption. However, pregelatinized starch hydrates in aqueous fluids and forms a paste, thereby exhibiting a gummy character which limits the desirability of this agent for skin care formulations. Furthermore, the equilibrium moisture content (or absorptivity) of pregelatinized starch at 25.degree. C. and 100% relative humidity is only about 40% greater than that of topical starch, which further limits the utility of this material.
Various other ingredients, including surfactants, humectants, cellulose, various polymers and the like, have been incorporated into powder compositions for the purpose of improving their skin feel. See, for example, Nichols (U.S. Pat. No. 5,209,932); Kurisaki et al. (U.S. Pat. No. 5,024,831); and Pugh et al. (U.S. Pat. No. 4,954,334). Cellulose does not aggregate on the skin thus providing a loose sensation to the user. Furthermore, cellulose absorbs residual moisture present on the surface of the skin, resulting in an overly dry sensation to the user. Swelling and shrinking of cellulose occurs due to excess or low content of moisture in the air, respectively. Such moisture sensitivity causes cracking during or after shaping. Sodium carboxymethyl cellulose is used in a number of compositions, including a topical detergent (Birtwistle et al., U.S. Pat. No. 5,180,579), a deodorant/antiperspirant (Faryniarz et al., U.S. Pat. No. 5,135,747), dispersible tablets (Milovac et al., U.S. Pat. No. 5,047,247) and a cosmetic base (Goode et al., U.S. Pat. No. 4,946,832). Moffett (U.S. Pat. No. 3,624,200) uses talc and starch as carriers in a composition for controlling perspiration odors on human skin. Synthetic resins have also been used; however, these tend to excessively agglomerate due to their capacity to accumulate triboelectric charge. Such agglomeration causes the powder to stand out after application to the skin. The term "stand out" refers to the appearance of a powder composition after application to the skin. A composition that "stands out" is readily apparent to visual inspection: the composition may cover the skin surface so that powder-coated areas are distinguishable from non-coated areas.
Others have designed microporous cellulosic powders specifically to enhance moisture absorption in skin preparations (Nichols, U.S. Pat. No. 5,209,932). The disadvantage of such systems is that they are not usually readily available and many lack a history of safe use in humans.
Callingham (U.S. Pat. No. 4,650,670) discloses powder compositions containing certain non-cellulosic polysaccharides, including chemically modified starches and cross-linked polyvinylpyrrolidone, in order to obtain increased moisture absorbency. In particular, the non-cellulosic polysaccharides are said to be capable of absorbing an amount of moisture at least equal to their own weight.
Despite the wide variety of known body powder compositions, there is a need for a moisture-absorbing composition that overcomes the difficulties inherent in the prior art (poor skin feel, caking, agglomeration, and the like). An ideal composition for topical use should be made of safe, readily available materials, be able to disperse easily onto the skin, carry a high payload of active ingredients, have acceptable tactile properties, and be capable of absorbing a large quantity of moisture without caking or standing out on the skin.
"Super disintegrants" is a term used in the pharmaceutical industry to describe a class of readily available materials, which are widely employed in pharmaceutical dosage forms, principally in ingestible tablets and capsules. The function of these compounds is to facilitate the break-up of tablets and capsules after ingestion. Croscarmellose sodium, starch sodium glycolate and crospovidone are three common super disintegrants. (Remington: The Science and Practice of Pharmacy, 19th ed., Mack Publishing Co., vol. II, p. 1619 (1995)). Starch sodium glycolate is an insoluble low substituted carboxymethyl ether of poly-alpha-glucopyranose obtained by treatment of potato starch. Crospovidone is an insoluble cross-linked polyvinylpyrrolidone.